Upgrade to HttpClient 4.2.1.
Change metrics-httpclient to be in line with 4.2.
Update release notes.
Handle long periods of inactivity without messing up forward decay priority sampling.
Clean up ExponentiallyDecayingSample and its tests.
Update release notes.
Merge pull request #235 from berngp/master

JMX Reporter: Avoid javax.management.InstanceAlreadyExistsException when registering.
Update release notes.
Stop caching a histogram's arrays.
Upgrade simplespec.
Remove my old repo.
Downgrade Hamcrest matchers.

Getting a bunch of NoSuchMethodError exceptions with 1.3. Will they ever get their shit together?
Add support for formatted messages to HealthChecks

This adds convencience methods to automatically format `HealthCheck`
messages using `String.format(format, args)`:

For healthy `HeathChecks`:
```java
Result.healthy("latency: %d", latency);
```

For unhealthy `HealthCheck`s:
```java
Result.unhealthy("timed out after %dms, connecting to %s:%d",
    timeout, host, port);
```
Fix link in docs.
Add DnsResolver param to InstrumentedClientConnManager.
[maven-release-plugin] prepare release v2.1.3
[maven-release-plugin] prepare for next development iteration
Update release notes.
add osgi manifest headers via maven-bundle-plugin
Add release notes.